Postnatal changes in sialylation of glycoproteins in rat liver

Abstract

Glycoproteins containing N-linked oligosaccharides were prepared from plasma and liver microsomes of rats aged 0-5 weeks, and galactose and sialic acid content were determined. The sialic acid/galactose ratios in plasma membrane N-glycans remained at about 1 throughout the postnatal period, suggesting that most of the galactose residues are sialylated. In the same way, it was suggested that most of the galactose residues of microsomal N-glycans were sialylated at 0, 4 and 5 weeks of age, but that the degree of sialylation was lower at the other ages, with a minimum at 2 weeks. When the activities of sialyltransferase and galactosyltransferase in liver Golgi membranes were determined, age-dependent changes were found, not only in the specific activities of the enzymes, but also in the Golgi membrane content per g of liver. The activity of galactosyltransferase per g of liver increased immediately after birth, whereas that of sialyltransferase remained at a low level for 2 weeks and then increased to a constant level at 4 weeks. It is probable that this delayed increase in the activity of sialyltransferase results in the decreased sialylation of microsomal N-glycans at 1, 2 and 3 weeks. Sialyltransferase was solubilized from the liver microsomes of rats aged 2, 3 and 4 weeks and characterized. Phosphocellulose column chromatography separated the activity into two subfractions, designated transferase I and transferase II in the order of elution. The increase in total sialyltransferase activity during this period was caused mainly by an increase in transferase I. Rechromatography of each transferase from 3-week-old rats after neuraminidase treatment showed that transferase I but not transferase II contained sialic acid residue(s) and that desialylated transferase I was eluted in a similar way as transferase II. Although the apparent Km value for CMP-N-acetylneuraminic acid and the heat stability of transferase I were different from those of transferase II, the difference was abolished by treating transferase I with neuraminidase, suggesting that transferase II may be a desialylated form of transferase I. These changes in the sialylation of membrane glycoproteins, including sialyltransferase, may be related to the control of liver growth during postnatal development.

Survival Signals of Hepatic Stellate Cells in Liver Regeneration Are Regulated by Glycosylation Changes in Rat Vitronectin, Especially Decreased Sialylation

“…We found that plasma VN obtained from PH rats had low carbohydrate concentrations, suggesting that PH-VN was less glycosylated (15). The decreased N-glycosylation of VN at 24 h after partial hepatectomy could be attributed to the attenuation of the oligosaccharide transferase activity in microsomes (31,32), which also causes the decrease of total glycoprotein synthesis in regenerating liver (33). In the early stage after partial hepatectomy, amounts of several kinds of fucosylated glycoprotein were reported to increase (34).…”

Comparison of oxidative stress biomarkers in renal tissues of d-galactose induced, naturally aged and young rats

“…It has been shown that SA residues which occupy terminal positions in N-linked oligosaccharides of glycoproteins play important roles in various biological functions (Oda-Tamai et al 1991). Desialylation shows its effect not only by altering the structure and function of glycoproteins, but also by increasing the amount of free SA levels which leads to emergence of pathologies in tissues (Goswami and Koner 2002).…”

N-Linked Glycosylation Is Not Essential for Sodium Taurocholate Cotransporting Polypeptide To Mediate Hepatitis B Virus Infection In Vitro

“…1B) revealed no mutation in the NTCP glycosylation site, the lack of N-linked glycosylation cannot be explained by NTCP itself. Enzymes involved in protein glycosylation, such as galactosyl transferase and sialyl transferase, undergo ontogenic regulation (22,23). Rat NTCP produced in the first 4 weeks of life was underglycosylated as a 39-kDa species rather than the 50-kDa species found in adult liver, with both species converted to a 33-kDa form following treatment with N-glycanase (24).…”